A separator of a battery in an electrochemical device is significantly important for improving stability, life and performance of the battery. Main functions of the separator are to provide a moving path of ions in the battery and to prevent physical contact between an anode and a cathode. Properties of the separator may be improved to manufacture a battery having excellent performance.
In order to improve the properties of the separator used in the battery, a multilayer separator formed by stacking a porous polymer such as a polyolefin-based polymer or a polypropylene-based polymer, or a separator including a coating layer formed by mixing a binder and inorganic particles, etc., while using the porous polymer as a substrate has been developed. The multilayer separator or the coating layer mixed with the binder, etc., may improve various properties of the separator as compared to a single layer separator. However, a thickness of the separator may be increased, and the performance of the battery may be rather reduced due to low permeability, reduction in wettability, and deterioration of impregnability.
As described above, it is difficult to manufacture a separator capable of having various properties that are sufficiently suitable for the separator of the battery, having a thin thickness, and satisfying mechanical and chemical stability to improve the performance of the battery. U.S. Patent Application Publication No. 2013-0037312 discloses a separator having excellent heat shrinkage by depositing alumina on a monolayer porous polymer substrate through a gaseous metal precursor. However, in this patent document, improvement in battery performance according to improvement in the heat shrinkage was not significantly increased.